1. Field of the Invention
The present invention relates to liquid discharging apparatuses and cleaning systems for the same, which discharge ink or liquids, such as printability improvers, onto recording media and are capable of forming high quality images.
The present invention is applicable to all the devices using recording media such as paper, cloth, unwoven fabric, and transparency sheets (OHP sheets). Examples of the devices include business machines and mass-produced machines, such as printers, copying machines and facsimiles.
2. Description of the Related Art
Ink jet recording has been used in printers, copying machines and the like due to low operation noise, low operation cost, easy size reduction, and easy color printing.
Conventional ink jet recording systems have the following inherent drawback. These systems discharge ink droplets onto a recording medium, such as paper and OHP sheet, through recording heads to record data. Fine ink droplets or mist forming when main ink droplets are discharged and ink droplets rebounded from the recording medium adhere to the discharging face of the recording head. The adhered ink will deposit around the nozzles and will clog some of them by means of adhesion of foreign matter such as powdered paper. Such nozzle clogging will cause deflection of ink discharge from the given direction and failure of ink discharge or ink non-discharge in severe cases.
The ink jet recording systems are therefore provided with recovery means to prevent these phenomena. Japanese Utility Model Laid-Open No. 58-128034 discloses, as shown in FIG. 30B, a configuration for wiping the adhered ink and foreign matters such as powdered paper on the nozzle face 208b, in which the top end of an elastic plate blade 208a is in contact with the nozzle face 208b and wipes the nozzle face 208b in the direction of the arrow 208c. In such an ink jet head, however, the nozzle face 208b may be damaged due to rubbing with the powdered paper.
A countermeasure to such a drawback is to form an indented nozzle face on the ink jet head so that the nozzle face and the other face portions do not form the same face. The above-mentioned flexible plate blade, however, does not work well with the indented nozzle face as follows.
(1) The plate blade does not come into contact with the nozzle face and thus does not wipe the dirt from it due to the step between the ink discharging face and the other faces.
(2) Some dirt will slip through the plate blade during wiping due to unstable contact pressure caused by the step.
(3) Some dirt will slip through the plate blade during wiping since the plate blade is deformed due to forced contact with the indented nozzle face and thus the contact pressure varies considerably depending on its position.
A countermeasure to the above-mentioned drawbacks of the indented nozzle face is disclosed by, for example, Japanese Utility Model Laid-Open No. 3-262646 as shown in FIG. 31A which is a sectional view of a nozzle face of a recording head and two types of cleaning members and FIG. 31B, which is a front view of such a configuration when viewed from the bottom side in FIG. 31A.
A cleaning member 209 consists of a first cleaning member 209a cleaning a nozzle face 209d which includes a nozzle 209e and a second cleaning member 209b cleaning ink-adhered portions 209c other than the nozzle face 209d. The first cleaning member 209a has a height which permits contact with the indented nozzle face 209d as shown in FIG. 31A and a width which is equal to the width of a nozzle array 209e as shown in FIG. 31B. The first cleaning member 209a moves in the direction of the arrow 209f and can clean the entire nozzle array 209e. On the other hand, the second cleaning member 209b has a height which permits contact with the ink-adhered portions 209c other than the nozzle face 209d as shown in FIG. 31A and can clean the ink-adhered portions 209c. In this case, the second cleaning member 209b consists of two fragments which are offset from the first cleaning member 209a in the direction of the arrow 209f and are arranged at both sides of the nozzle array 209e. Such a configuration having two types of cleaning members permits perfect cleaning of the nozzles and other faces of the recording head which do not form the same face.
Another countermeasure is shown in FIG. 32A which is a sectional view of a nozzle face of a recording head and two types of cleaning members and FIG. 32B, which is a front view of such a configuration when viewed from the bottom side in FIG. 32A. A first cleaning member 210a shown in FIGS. 32A and 32B is substantially equal to the first cleaning member 209a of the above-mentioned countermeasure. The second cleaning member 210b, however, differs from the second cleaning member 209b of the above-mentioned countermeasure in that it is not divided into two fragments.
In the countermeasures shown in FIGS. 31A and 31B and FIGS. 32A and 32B, wiping along the direction perpendicular to the nozzle array, that is, in the direction of the arrow 209f or 210f, may adversely affect ink discharge characteristics. Typical examples of such cases include recording using a printability improving solution which instantaneously makes the dyes insoluble and coagulates dyes in the ink and recording using a pigment ink or the like in which fine particles are dispersed.
FIG. 33 is a front view illustrating an ink discharging state by a recording head having a nozzle array for the printability improving solution, wherein 211a is a discharging head for the printability improving solution, 211b is an ink head or recording head, and 211c is a recording medium. The discharging head 211a for the printability improving solution has a solution nozzle array 211d, the ink head 211b has an ink nozzle array 211e, and these two heads are adjacent to each other in the scanning direction shown by the arrow 211i. The discharging head 211a for the printability improving solution discharges a droplet 211j of the printability improving solution on a predetermined position of the recording medium 211c to form an adhered layer 211k. Next, an ink droplet 211l is discharged on the adhered layer 211k of the printability improving solution to form a coagulated region 211 m by instantaneous coagulation of the ink. Such a system can improve the image quality by preventing ink bleeding between different colors and by endowing waterproof properties.
In this system, however, the ink is discharged onto the adhered layer 211k of the printability improving solution which is previously discharged on the recording medium 211c, hence a mixed mist of the printability improving solution and the ink will rebound and adhere near the ink nozzle array 211e to form a coagulate 211h. Adhered layers 211f and 211g of the mists from the printability improving solution and the ink may also be formed on the nozzle arrays 211d and 211e, respectively.
FIG. 34 is an enlarged plan view of the head shown in FIG. 33 from the recording medium side, which shows regions in which the mists from the ink and the printability improving solution adhere onto the faces including the ink nozzle array. As shown in FIG. 34, on the face of the ink head the mist of the ink adheres to a region 211g near the nozzle array 211e during discharging the ink, whereas a mixed mist 211n of the printability improving solution and the ink adheres to the periphery of the nozzle array 211e to form the coagulate 211h. When wiping is performed in the direction perpendicular to the nozzle array as shown in FIGS. 31 and 32, the coagulate 211h shown in FIG. 34 is squeezed into the nozzles. As a result, the quality of the printed image will decrease due to deflection of the discharged ink and non-discharge of the ink. Further, the coagulate squeezed into the nozzles cannot be removed by preliminary discharge of the ink after wiping, hence the image quality cannot recover from the deterioration. A measure is therefore required to prevent squeezing of the coagulate into the nozzles due to wiping along the nozzle array.
In particular, since the nozzle face and the other faces do not form the same face in the above-mentioned system, the indented nozzle face 213c (FIG. 35A) does not come into perfect contact with the top of the flexible plate blade 213a during wiping the nozzle face 213c along the nozzle array. As a result, the dust, powdered paper, adhered ink drops, the sticky solid component formed by drying the ink and, in particular, coagulate of the printability improving solution and the ink cannot be removed from the face near the nozzles. FIG. 35A is an outlined front view of a flexible plate blade wiping the bottom of the indented head face 213c including the nozzle face, and FIG. 35B is an outlined front view of a small flexible plate blade wiping only the nozzle face at the bottom of the indented head face.
In order to solve such drawbacks, the present inventors have tried wiping of the indented nozzle of the ink head along the longitudinal direction using a cleaner including a flexible wiper and a rubbing member disclosed in Japanese Utility Model Laid-Open No. 61-5647 and Japanese Patent Laid-Open No. 4-338552. The flexible wiper, however, did not come into contact with the indented nozzle face. The present inventors, therefore, have tried cleaning using only the rubbing member. Although this cleaning process is effective at an initial stage, the following drawbacks arise after repeated cycles of use.
(1) In the above-mentioned ink head, the coagulate and thickened ink gradually deposit on the surface of the rubbing member by the reaction of the ink with the printability improving solution during repeated cycles of cleaning of the face using only the rubbing member, and the deposited coagulate is retransferred to the ink jet head and squeezed into the nozzles, resulting in deflection of the discharged ink and deterioration of printing.
(2) In the discharging head for the printability improving solution, not only the printability improving solution but also the ink gradually deposit on the rubbing member during repeated cycles of cleaning of the face using only the rubbing member, and the surface of the rubbing member is covered by the coagulate of the printability improving solution and the ink. The deposited coagulate is barely removed by the rubbing member and is readily retransferred from the rubbing member to the face.
The water repellency of the face is perfectly lost by retransferring cycles, during which a large amount of printability improving solution adheres onto the face after aspiration. As a result, the deposited printability improving solution causes deflection of the discharged ink and deterioration of printing.
In addition to the deposition of the ink, the ink dye and fibrous materials also deposit on the nozzle face 208b of the ink jet recording head, as shown in FIG. 30, by evaporation of the solvent in the ink. A measure suitable for removing such contamination is a cleaning member composed of a porous wet elastic member disclosed in Japanese Utility Model Laid-Open No. 58-128034. Although the cleaner is smeared by repeated cleaning operation in such a cleaning system, hence the cleaning effect gradually decreases.
Ink jet recording apparatuses each provided with two cleaners, i.e., a wiper and a cleaning means are proposed. For example, FIG. 36 shows an ink jet recording apparatus provided with a wiper 32 and a cleaning means 33 proposed in Japanese Patent Laid-Open No. 2-518. Further, FIGS. 37A and 37B show an ink jet recording apparatus provided with a cleaner composed of a cleaning member 33 made of a wet porous elastic member and a protruded wiper 32 which is disclosed in Japanese Utility Model Laid-Open No. 61-5647. FIGS. 38A, 38B and 38C show an ink jet recording apparatus provided with a cleaner disclosed in Japanese Patent Laid-Open No. 4-338552 in which a wiper 32 and a water absorbable cleaning member 33 are bonded to each other with a bonding agent 81.
In the ink jet recording apparatus shown in FIG. 36, however, the cleaning means has a complicated configuration due to independent location of the wiper 32 and the cleaning member 33, hence the operation is also complicated. Since the stiffness of the cleaning member 33 is generally low, the cleaning member 33 must have a relatively large size in order to achieve a sufficient contact pressure by the cleaning member itself, and such a cleaning member 33 does not fit well to an irregular nozzle surface. In contrast, if the thickness of the cleaning member is reduced so that the cleaning member fits sufficiently to the nozzle surface, a satisfactory contact pressure cannot be achieved.
In the ink jet recording apparatus shown in FIGS. 37A and 37B, the cleaning member 33 does not form a sufficient contact pressure and thus does not cause a satisfactory result. In some case, the cleaning member 33 is not wet enough to form a suitable contact pressure. Further, the cleaner is frequently used and requires high durability.
The ink jet recording apparatus shown in FIGS. 38A to 38C requires an additional step for bonding the cleaning member 33 and the wiper 32 and has drawbacks such as the durability of the joint between them and the selection of the bonding agent. In the wiping of an indented nozzle face 213c with a wiper shown in FIG. 38B in the nozzle array direction, the wiper 32 does not substantially come into contact with the nozzle face as in the case shown in FIG. 35A.